They should only contain stripped PDBs.

For instance, Editor\Data\PlaybackEngines\windowsstandalonesupport\Variations\win32_development_il2cpp contains these PDB files:

UnityPlayer_Win32_development_x86_il2cpp.pdb
UnityPlayer_Win32_development_x86_il2cpp_s.pdb
WindowsPlayer_x86_Release_il2cpp.pdb
WindowsPlayer_x86_Release_il2cpp_s.pdb

While Editor\Data\PlaybackEngines\windowsstandalonesupport\Variations\win32_development_mono contains these PDB files:

UnityPlayer_Win32_development_x86_mono.pdb
WindowsPlayer_x86_Release_mono.pdb

The mono PDB files are actually the "_s" variants (they're much smaller). That's how it should be in IL2CPP folder too. We upload our full PDBs to the symbol server anyway (we should actually verify that it's the case), so we don't need to keep them in the installer.